Abstract

Experiments were carried out to investigate the influence of combined nitrogen (N) and sulphur (S) fertility on the organosulphur compound content of garlic bulbs, especially alliin, as a specific flavour quality trait related to the health-value of garlic. Three cultivars, 'Printanor', 'Morasol' and 'Messidr6me', were grown in the greenhouse and in vitro. Sulphur was increased in the macronutrients within the range 0 - 144 mg l(-1). Numerous combinations of both S and N were tested in vitro. In the greenhouse, increasing N levels, from 184.8 mg l(-1) to 856.8 mg l(-1), were tested with a single high level of S (128 mg l(-1)). Increasing S alone did not affect the growth or bulb weight of any garlic cultivar, but slightly increased the alliin content of bulbs. No symptoms of S deficiency were observed under greenhouse conditions, although the same garlic cultivars grown in vitro at 0 mg S l(-1) clearly suffered, their size being greatly reduced. This suggests an important role for S contamination, such as atmospheric S, in the process of S absorption by garlic plants, which is discussed. Increasing N levels significantly accelerated garlic maturity and decreased bulb yield. The effect of N on the organosulphur compound content of bulbs was cultivar-dependent, but alliin accumulation was not enhanced. 'Printanor' and 'Morasol' had the highest alliin levels and were negatively influenced by increasing N, while a slight synergistic effect of S and N was observed on 'Messidrome'.'Messidrome' also had the highest flavour potential when including precursors, and was more efficient in accumulating S into organosulphur compounds. It is therefore advisable to choose the most appropriate variety, and to adapt the N x S fertilisation regime according to the environment, in order to produce garlic with the highest health-value.